1. Field of the Invention
The present invention relates generally to supercontinuum light emitting devices and methods for generation of supercontinuum by using optical fibers.
2. Technical Background
It is known to generate supercontinuum by launching femtosecond duration (10−15 sec) pulses of light from the light source into the optical fiber segments. For example, the device disclosed in U.S. Pat. No. 6,775,447 utilizes an optical fiber having a plurality of nonlinear fiber sections. Those sections have zero dispersion wavelengths that are within ±200 nm of the wavelength of the light source.
One of the drawbacks of the method disclosed in U.S. Pat. No. 6,775,447 is that it relies on very high peak pulse power (on the order of 10 KW or larger) to produce the supercontinuum. For example, this patent describes light pulses having about 15 KW of power (3 nJ/200×10−15 sec). However, typically the power available from CW (continuous wave) sources is of the order of a few watts. Therefore, this technique generally would not operate with typical CW light sources.
Another technique for generating a supercontinuum is described, for example, in the article entitled “Continuous-wave pumping in the anomalous- and normal dispersion regimes of nonlinear fibers for supercontinuum generation” by A. K. Abeeluck and C. Headley [in Optics Letters, Vol. 20, No. 1, pp. 1, pp. 61–63]. This reference discloses a CW pumping of a nonlinear fiber, such that the wavelength of the source is only a few nanometers away from the zero dispersion wavelength of the non-linear fiber. Having the wavelength of the source so close to the zero dispersion wavelength of the fiber creates spectral broadening via four wave mixing phenomena. However, FIG. 1 of this reference shows that the stimulated Raman scattering (SRS) causes the resulting broadening to be strongly asymmetric, with most power extending to the longer wavelength range. Therefore, at some distance from the input end of the fiber, most of the propagating light power is in the wavelength range far from the zero dispersion wavelength, diminishing the efficiency of four wave mixing.
Therefore, there is still a need to generate CW supercontinum in a more efficient manner.